Electronic modules, such as radio frequency (RF) modules, typically contain RF circuits, transmission lines, high power amplifiers, and antenna elements that are commonly manufactured on specially designed substrate boards. For the purposes of such circuits, it is important to maintain control over impedance characteristics. If the impedance of different parts of the circuit do not match, this may result in inefficient power transfer, unnecessary heating of components, or various other problems. To minimize these problems, a transmission line impedance transformer matching network is commonly utilized in such circuits, for example, to match relatively low impedances at the gate and drain of field effect transistors (FETs) in the circuit with relatively high impedances needed in other parts of the circuit.
One factor affecting the performance of such transmission line impedance transformer matching networks is the dielectric property of the impedance transformer substrate medium, such as the dielectric constant of the medium. For example, the dielectric constant of the substrate medium affects the velocity of the signal propagating through the medium, and therefore the electrical length of the transmission line. In conventional RF design, an impedance transformer substrate medium is typically selected with a dielectric property value suitable for the design. Once the substrate material is selected, the transmission line characteristic impedance value may be exclusively adjusted by controlling the impedance transformer geometry and physical structure.
As the trend toward miniaturizing such RF modules and circuits continues, the ability to maintain the performance attributes of such circuits becomes increasingly difficult. For example, increasing the power and bandwidth of a high-power amplifier used in an RF circuit may be a common design criteria, but enhancing these attributes while maintaining a compact size of the circuit is difficult, if not often impractical. For example, while a transmission line transformer output matching network may be utilized to provide good bandwidth and excellent power output for the amplifier, such utilization is often at the expense of increased size and fabrication difficulty of the impedance transformer and circuit. As such, designers will typically be forced to trade one desired specification (e.g., power, bandwidth, size, or fabrication difficulty) so as to satisfy another one of these desired specifications.